Messages

921

General Mach Discussion / Re: Whose Fault Is ThIs?

« on: December 02, 2009, 07:53:44 AM »

This sounds eerily familiar


If someone is working on this problem, they should also consider that this behavior is present on, or is triggered by the A axis.

Under certain conditions, if the A axis and the X axis (for example) start moving together, MACH ignores acceleration and just slams the X axis from zero to feedrate. I don't recall off hand the circumstances, but I posted some details on this quite some time ago.

Sounds like this may be a symptom of the same bug, so I thought it worth mentioning.

922

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: November 25, 2009, 05:26:11 AM »

Hi Steve,

. . . . . a step/Dir interface is a reletive one, as opposed to an absolute one. With step/ Dir, it is move this increment from where I am.

Peter.

The drive maintains an absolute position internally. Some drives have a built in homing capability, which one might assume would complicate a 'roll over' of the position register, but I have no experience with those drives, so I don't know how they address that issue.

I find that there is no standard criteria in designing servo drives (speaking only of those that I tested). One manuf may consider an internal homing ability more important than continuous running, if in fact that is the trade off, while another may decide the opposite. Leadshine, as an example, thinks in terms of OEM only and concludes therefor that the ability to reset a faulted drive is not an important issue, because (in their view) once the specific 'single purpose' of a machine is set up properly, there should be no faulting. This unfortunate thinking leaves the Leadshine drives usesless for a 'general purpose' machine tool, in my opinion, even though they are otherwise very good drives.

These are the kinds of differences that make evaluating and selecting a drive much more complicated than is generally thought. Your 'continuous running' question is a very good and valid one that did not surface during my review unfortunately, so I did not investigate that ability in each drive. It is a caveat for sure.

923

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: November 23, 2009, 04:34:56 AM »

Hi Mike,

After reading your excellent trade study on servo drives, I've just ordered a Dugong Servo drive that I plan to use to drive my Lathe spindle which is a 400W 90Vdc motor.I've just had a thought. Do you know if the Dugong drive capable of being continuously run in 1 direction? Some servo drives fault after running too far in one direction.
Cheers,
Peter.

Peter, I suspect you are addressing that question to me, so I should tell you my first name is Steve.

There must be some upper limit of encoder counts that the drive can handle, but I have not found it yet. Good question . .  I'll get an answer to this and post it.

EDIT: The answer is no, the register is 32 bits wide and rolls over when full so the drive will never fault from running on one direction too long.

One reason I liked the Dugong for a spindle drive is the built in braking resistor. A heavy chuck and workpiece can generate a lot of back current and the Dugong dumps it overboard instead of burning out the the drive. Using a servo motor on the spindle eliminates all of the threading problems and also opens the door for some interesting possibilities with cutting tools and grinding wheels attached to the cross slide, yes?

Incidentally, I have one of your excellent PWM speed controllers, which finally solved my speed control problems. Unfortunately, I can't use it with my 4th axis because of the swap axis function . . .  .

924

General Mach Discussion / Re: Problem with XBOX 360 Pendant...?

« on: November 20, 2009, 11:19:53 AM »

Perhaps it boils down to the frequency of the wireless device vs the speed Mach is running.

There are lots of differnet wireless net frequencies, which may explain why some have trouble and some not.

I am not an electronics guy so for the most part, electronics problems are solved using the Vaudeville solution:

Patient: "Doc, it hurts whenever I do this"

Doc: "Then don't do that,  . . . next!"

925

General Mach Discussion / Re: Problem with XBOX 360 Pendant...?

« on: November 19, 2009, 04:53:20 PM »

Just FYI, there are two different animals in the barn.

The wireless network interface and the wireless Xbox controller interface.

I also used the Micro$oft brand Xbox controller specific wireless USB transceiver.

Both caused havoc with the CNC controls. You may have good luck with the wireless Xbox controller. The good thing is that if you do have any problems, the wired controller is inexpensive and works just as good, so you can eliminate the RF if needed and still have the nice control feature.

926

General Mach Discussion / Re: What motor size and driver should I use

« on: November 19, 2009, 04:43:53 PM »

I can second the recommendation for the HomeshopCNC servo motor. Note that is it similar to the Keling drive, but 72V instead of 90V. USdigital or Aveco encoders work well.

My enthusiasm for the Gecko stepper drives does not extend to their servo drives. The Geckos have very crude tuning and they 'sing' or bounce between encoder counts constantly, which is quite annoying. The functional problem is that their low bandwidth chokes the motor RPM with a high resolution encoder.

In any case, a 20A drive is not the best match for that motor (in my opinion), as you loose a lot of acceleration with the 20A limit. I ran that very motor thru its paces with the Gecko320/340 and several other drives and there is a very big difference in the preformance. You can read the review here: http://www.thecubestudio.com/ServoDriveReview.htm Pay particular attention to the braking resistor issue with larger motors.

My preference is for the CNCdrive Dugong servo drive, which I use with the NEMA34 motor referenced earlier.  I have 5 of them now and am quite happy with the features, especially the tuning software. The only issue is availability. They are often sold out.

927

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: November 19, 2009, 04:10:25 PM »

I am getting multiple inquiries on programming for the 4th axis and as much as I would like to I cannot always respond individually. I do try to respond to notices from this forum, so posting questions here is the best route.  Here are the answers to the most FAQ:

Everything you see in the videos is using strictly the Mach mill program, never the turning program. There is only one setup and one profile. I wrote a simple macro to implement the MACH 'swapaxis' function to run the 4th axis as a spindle. (thanks goes to Hood for this tip). I recently learned to also turn on the mill spindle while the 4th axis was still in 'spindle' mode. You see that with the grinding video.

I also wrote macros to calculate and perform threading. I participated a bit in discussing theory on the threading topic but in practice I do not use the Mach threading, so unfortunately I can't help with that.

Primarily I design assemblies in AutoCAD and then isolate the parts, move them to 0,0 and dxfout the geometry of each part in this way. Then using LazyCAM to pick up the dxf and generate the basic Gcode. I then usually find it convenient to make resulting 'programs' into subroutines and set up variables and write a small 'control header' to call the subroutines in order, and that is pretty much the technique.

Turning profiles are sometimes generated for MachTurn and then run on the mill by swapping the axis around with a G-code command for that part of the program, again usually called as a sub. Sometimes it is easier to lift a turning profile directly off the design in AutoCAD and then simply generate code from that profile for the Z axis.

928

General Mach Discussion / Re: List of suitable PCI parallel ports

« on: November 19, 2009, 03:05:26 PM »

If you do a search here on the forum you will find a post I made with the exact card, drivers, source and instructions on how to add a MACH compatible PCI port card.

929

General Mach Discussion / Re: re reference after e stop/limit switch

« on: November 19, 2009, 02:53:51 PM »

There is little commonality between differnet servo drives. They each have their own way of behaving approaching, during and after faulting.

Some drives will fault and cut power to the motor, but continue to track the encoder and the control inputs and therefor can remain 'homed' even if the motor is stopped. Correcting the fault sends the axis back to the correct location.

You may find a review of various drive beneficial. You can find it with a search on this forum. ALL of the drives I tested do behave the same in one characteristic and that is that a reset, however initiated, causes the drive to loose 'home' and re homing is needed.

In my setup, I have the drive error lines connected individually to the Mach axis limits, but I usually have soft limits active so a limit fault means one of the servos is faulted (usually). Mach is vague about why it stops, but I have remote indicator lights on each servo drive so that I know which one faulted and I have separate reset buttons next to the indicators so I can reset each drive independently.

Still, in practice, I have to say that I agree completely with Hood in that it is safer to just re-home all axis after a fault, just to be on the safe side . . . provided, of course that your fixture setup allows this to happen conveniently. I am finally tuned up pretty well and the only faults I have these days is with stopping a program mid run that has multiple coord offsets in it or when I am debugging a program and where I sometimes have to turn soft liimts off if Mach gets confused by all the shifting around (or maybe it's me that gets confuded . . )

930

General Mach Discussion / Re: What motor size and driver should I use

« on: November 19, 2009, 02:39:46 PM »

I have to second the notion to avoid multi axis setups.

For steppers, I have to also second using big steppers as noted by Hood on his machine. Definitely 900 oz-in or better.

For stepper drives, I can confidently recommend the Gecko203V (their top-of-the-line). My preference from those I have used is the Centent commercial drives. Noticeably better than the Gecko  . . .  and noticeably more expensive as well.

DC brush Servo setups are now comparable in price to steppers for mid to larger machines if you accurately compare the real world performance power wise. In my opinion, there is no reasonable comparison performance wise. The two types are worlds apart in their characteristics.